A selective replication of a specific gene or genes disproportionate to their representation in the parent molecule; such as, that which occurs in specific cells in response to signals of cell development or to stresses from the environment: "In humans, gene amplification is seen more often in malignant cells."

In genetics, a hereditary unit consisting of a sequence of DNA which codes for a specialized function: Luxury genes are sometimes synthesized; usually, in large amounts, in particular cell types.

A gene which allows the normal functioning of gametes (reproductive cells in animals and plants), but has deadly effects during embryonic or larval development: A zygotic lethal gene is a changed or an altered version of a healthy gene, which is necessary for viability of a zygote, and causes a deletion or loss of the entire gene.